The invention relates to analysis of xerographic processes, and more particularly, to the precise determination of failed parts within the xerographic process.
As reproduction machines such as copiers and printers become more complex and versatile, the interface between the machine and the service representative must necessarily be expanded if full and efficient trouble shooting of the machine is to be realized. A suitable interface must not only provide the controls, displays, fault codes, and fault histories necessary to monitor and maintain the machine, but must do so in an efficient, relatively simple, and straightforward way. In addition, the machine must be capable of in depth self analysis and either automatic correction or specific identification of part failure to minimize service time.
Diagnostic methods often require that a service representative perform an analysis of the problem. For example, problems with paper movement in a machine can occur in different locations and occur because of various machine conditions or failure of various components. In the prior art, this analysis by the service representative has been assisted by recording fault histories in the machine control to be available for readout and analysis. For example, U.S. Pat. No. 5,023,817, assigned to the same assignee as the present invention, discloses a method for recording and displaying in a finite buffer, called a last 50 fault list, machine faults as well as fault trends or near fault conditions. This data is helpful in diagnosing a machine. It is also known in the prior art, to provide a much larger data log, known as an occurrence log, to record a variety of machine events.
In addition U.S. Pat. No. 5,023,817, assigned to the same assignee as the present invention, discloses a technique to diagnose a declared machine fault or a suspected machine fault by access to a library of fault analysis information and the option to enter fault codes to display potential machine defects related to the fault codes. It is also known, as disclosed in U.S. Pat. No. 5,533,193 to save data related to given machine events by selectively setting the control to respond to the occurrence of a given machine fault or event, monitoring the operation of the machine for the occurrence of the given machine event, and initiating the transfer of the data in a buffer to a non-volatile memory.
It is also known to be able to monitor the operation of a machine from a remote source by use of a powerful host computer having advanced, high level diagnostic capabilities. These systems have the capability to interact remotely with the machines being monitored to receive automatically initiated or user initiated requests for diagnosis and to interact with the requesting machine to receive stored data to enable higher level diagnostic analysis. Such systems are shown in U.S. Pat. Nos. 5,038,319, and 5,057,866 owned by the assignee of the present invention. These systems employ Remote Interactive Communications to enable transfer of selected machine operating data (referred to as machine physical data) to the remote site at which the host computer is located, through a suitable communication channel. The machine physical data may be transmitted from a monitored document system to the remote site automatically at predetermined times and/or response to a specific request from the host computer.
The host computer may include a compiler to allow communication with a plurality of different types of machines and an expert diagnostic system that performs higher level analysis of the machine physical data than is available from the diagnostic system in the machine. After analysis, the expert system can provide an instruction message which can be utilized by the machine operator at the site of the document system to overcome a fault. Alternatively, if the expert system determines that more serious repair is necessary or a preventive repair is desirable, a message can be sent to a local field office giving a indication of the type of service action required.
Also, U.S. Pat. No. 5,636,008, assigned to the same assignee as the present invention, discloses a technique for remote access and diagnostic manipulation of a machine for improved preparation before making a service call.
It is expected that future office products could be serviced by a variety of individuals that could include the customer, representative of product manufactures, or third party service organizations. The service may include parts repair or replacements, adjustments or software updates and should be made as conveniently and readily available as possible. In order to meet this new level of convenient service in an ever complex set of products, it is necessary to provide rapid, easily interpretable information on the status of the machines, to those that are likely to service the product.
The use of expert systems discussed above, are also well known in the art. For example, it is known to provide a computer controlled diagnostic apparatus for industrial or other types of operating systems. A rule base pertinent to the particular operating system being diagnosed is stored in memory. The rule base is established by experts in the field to which the diagnosis pertains. Sensors monitor operating parameters of the system and provide output signals which are fed to the diagnostic apparatus. Indications of the overall "health" of the operating system in general and of its components in particular are provided to the user via a display. In addition, U.S. Pat. No. 5,138,377 discloses an internal expert system to aid in servicing which monitors predetermined status conditions of the machine for automatic correction or for communication to the user.
A difficulty with prior art diagnostic services is the inability to easily and automatically pinpoint the precise parts or subsystems in a machine causing a malfunction or deteriorating condition. It would be much more economical to be able to simply replace a part than to exert significant time and effort trying to correct or repair the part. This is the trend in today's high tech system environment. It would be desirable, therefore, to provide a highly intelligent, automated diagnostic system that provides an indication of the need to replace specific parts or subsystems rather than the need for extensive service troubleshooting to minimize machine downtime.
In copying or printing systems, such as a xerographic copier, laser printer, or inkjet printer, a common technique for monitoring the quality of prints is to artificially create a "test patch" of a predetermined desired density. The actual density of the printing material (toner or ink) in the test patch can then be optically measured to determine the effectiveness of the printing process in placing this printing material on the print sheet.
In the case of xerographic devices, such as a laser printer, the surface that is typically of most interest in determining the density of printing material thereon is the charge-retentive surface or photoreceptor, on which the electrostatic latent image is formed and subsequently, developed by causing toner particles to adhere to areas thereof that are charged in a particular way. In such a case, the optical device for determining the density of toner on the test patch, which is often referred to as a toner area coverage sensor or "densitometer", is disposed along the path of the photoreceptor, directly downstream of the development of the development unit. There is typically a routine within the operating system of the printer to periodically create test patches of a desired density at predetermined locations on the photoreceptor by deliberately causing the exposure system thereof to charge or discharge as necessary the surface at the location to a predetermined extent.
The test patch is then moved past the developer unit and the toner particles within the developer unit are caused to adhere to the test patch electrostatically. The denser the toner on the test patch, the darker the test patch will appear in optical testing. The developed test patch is moved past a densitometer disposed along the path of the photoreceptor, and the light absorption of the test patch is tested; the more light that is absorbed by the test patch, the denser the toner on the test patch. Xerographic test patches are traditionally printed in the interdocument zones on the photoreceptor. Generally each patch is about an inch square that is printed as a uniform solid half tone or background area. Thus, the traditional method of process controls involves scheduling solid area, uniform halftones or background in a test patch. Some of the high quality printers contain many test patches.
It would be desirable, therefore, to be able to use a simple toner area coverage sensor rather than a complex sensor system to provide machine data to be able to diagnose a machine and identify specific part or subsystem failures or malfunctions. It would also be desirable to provide a systematic, logical test analysis scheme to assess machine operation from a simple sensor system and to be able to pinpoint parts, components, and subsystems needing replacement.
It is an object of the present invention, therefore, to maintain uniform development on a photoreceptor surface by initiating a series of halftone test patches over the circumference of the photoreceptor surface and analyzing signals reflected from each of the halftone test patches by comparing the signals to reference signals in order to identify segments of the photoreceptor surface manifesting non-uniformity. Another object of the present invention is to provide a systematic, logical test analysis scheme to assess machine operation from a simple sensor system and to be able to pinpoint parts and components needing replacement.
Other advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.